Volatilisation of pesticides after foliar application in vegetable greenhouses

Volatilisation of pesticides after application to the soil or the crop is an important source of emission into the atmosphere. As a result, workers, residents and bystanders are potentially at risk when exposed to these volatilised substances. Nonetheless, data on measured concentrations are quite scarce, especially in greenhouses. The objective of this work is to present the results of volatilisation experiments performed in greenhouses. Results: The results indicate that the concentrations are highest in the hours after application and rapidly decline during the days following application. The volatilisation experiments were conducted in the greenhouse complex of the Research Station for Vegetable Production (RSVP) in Sint-Katelijne-Waver, Belgium. Two types of ventilation regimes were used during the course of the experiments. In the cucumber and tomato greenhouses, a mixture of Scala (400 g LU+22121 pyrimethanil, SC, BASF Belgium) and Corbel (750 g LU+22121 fenpropimorph, EC, BASF Belgium) was applied to the mature crop. Sampling units were placed in the centre of the treated area and in the main greenhouse aisle. At each location, sampling was done at two different heights: just above the crop and at breathing height. This resulted in sampling heights of approximately 1.5 m and 2.5m for tomato and cucumber, respectively. Concentrations of volatilised pesticides in the air were measured with an active sampling system. Fenpropimorph and pyrimethanil samples were analyzed by gas chromatography mass spectrometry (GC/MSD). In this study, measurable concentrations of fenpropimorph and pyrimethanil were found in the air for up to 4 days after application but sampling height seemed to have little effect on the pesticide concentration in the air. The concentrations of pyrimethanil and fenpropimorph were highest during the first hours after application and showed a considerable decrease in the days after application. Volatilisation of the applied substances is not the only process taking place in the plant environment after application. Competing processes such as penetration into the crop may take place and limit the volatilisation of the substances as well as additives present in the formulation. Greenhouse temperature, ventilation rate, the substance vapour pressure and the rate of competing processes were identified as important factors influencing volatilisation in greenhouses. Recently, the PEARL model has been extended to include volatilisation under glasshouse conditions. The results from this study could be used to test the model calculations against measured pesticide concentrations in greenhouse air. Analysis of the differences between measured and computed concentrations may indicate possibilities for model improvements. Moreover, the study results may identify processes that need further study. Computational models and experimental work will both be helpful to extend the current knowledge about volatilisation of plant protection products under varying conditions.

ISBN:9788862615082